This invention relates to an adaptive braking system for use on vehicles having fluid pressure actuated brakes.
Adaptive braking systems for vehicles having fluid pressure actuated brakes normally include a modulator which decreases braking pressure when an incipient skidding condition is detected and which also serves as the relay valve which communicates fluid pressure to the braking actuators during normal braking. In order to achieve the high vehicle deceleration rates during normal braking required by government regulations, modulators of the type discussed herein which also function as relay valves must have high flow rate capabilities. However, these high flow rates are normally detrimental to good adaptive braking performance, and consequently, most prior art modulators which also function as relay valves are provided with "pneumatic logic" to reduce the flow rate through the modulator during adaptive operation. Although these prior art modulators which incorporate "pneumatic logic" have, in general, performed acceptably, the "pneumatic logic" does increase the complexity of the modulator valve and consequently increases its cost. Furthermore, the "pneumatic logic" apparatus which must be included in the modulating valve normally includes relatively small flow-restricting orifices, which are susceptible to clogging by contaminants in the vehicle fluid pressure supply, thereby causing a failure in the adaptive braking system.